1. Field of the Invention
The present invention relates to a surface acoustic wave device used for resonators and bandpass filters and more particularly, to an edge reflection type surface acoustic wave device having a construction in which a Shear Horizontal (SH) type surface acoustic wave is reflected between two opposing end surfaces and a manufacturing method for the same.
2. Description of the Related Art
Various edge reflection type surface acoustic wave devices using of SH waves such as a BGS wave, a lobe wave, etc., reflected between confronting end surfaces have been proposed.
In the edge reflection type surface acoustic wave device, the SH wave is reflected between the opposing two end surfaces, and, in this case, there is a problem that, when unnecessary waves other than the SH waves are reflected at the end surfaces, undesired ripples appear in the characteristics and the deviation of GDT (group delay time characteristics) increases.
In Japanese Unexamined Patent Application Publication No. 4-82315, a construction in which a bulk wave producing unnecessary spurious noise is suppressed, is shown in an edge reflection type surface acoustic wave device. Here, stair portions are provided at a height which is a thickness portion of the piezoelectric substrate where 80% of the energy of the SH wave is concentrated or farther away from the surface of the piezoelectric substrate, on the opposing two end surfaces which are used as reflection end surfaces. The energy of a bulk wave spreads over the entire thickness area of the piezoelectric substrate, but, on the other hand, the energy of the SH wave is concentrated in a layer that is close to the surface of the piezoelectric substrate. Therefore, in this prior art device, the above-noted difference of deviation of the energy between the SH wave and a bulk wave is utilized and the resonance of the SH wave is effectively utilized in the layer of the piezoelectric substrate on the surface side of the piezoelectric substrate beyond the stair portion. On the other hand, the resonance of a bulk wave has no effect in the layer of the piezoelectric substrate that is lower than the stair, and accordingly, the spurious noise to be produced by a bulk wave is suppressed.
Furthermore, in this prior art, it is also shown that irregular reflection of a bulk wave is produced by making the end surface portions which are lower than the stair, a rough surface and, as a result, the resonance energy of a bulk wave is reduced.
However, in this prior art, it is also shown that it is not necessary to make the end surface portions which are lower than the stair a rough surface.
Furthermore, in FIG. 5 of the 4-82315, a construction in which second and third end surface portions are formed two stairs away from end surface portions provided on the side of the surface on which the electrodes of the piezoelectric substrate are formed and below the end surface portions, is shown, and here, it is also shown that, below each stair, the second and third end surface portions may be appropriately made to have a rough surface.
As disclosed in Japanese Unexamined Patent Application Publication No. 4-82315, in the past, a method in which, in an edge reflection type surface acoustic wave device, the end surfaces are made to have a rough surface in order to suppress the reflection of unnecessary waves such as a bulk wave, etc., on the end surfaces is shown. However, when two opposing end surfaces of a piezoelectric substrate are cut by using a blade under the condition that the end surfaces become a rough surface, there is a problem in that cracks are produced on the end surfaces and in that chipping is likely to occur in the edge portion between the end surface and the bottom surface of the piezoelectric substrate.
That is, it is very difficult to obtain an edge reflection type surface acoustic wave device in which ripples and spurious noise are fully suppressed and cracks, chipping, etc., are not produced.